1. Field of the Invention
The present invention relates to the processing of dried fruit containing pits. Examples of such fruit include, but are not limited to, dried plums (prunes), cherries, peaches, and apricots. Processing in this case refers to non-destructive on-line bulk testing as well as destructive testing for quality control sampling.
2. Background
The presence of pits and pit fragments in harvested fruit such as (but not limited to) dried plums is a matter of concern for processors, causing occasional rejection of product by retail chains as well as injury to consumers which can lead to lawsuits and money damages. In addition to these concerns, the presence of pits has a deleterious effect on the products' quality grade and therefore influences the prices that processors may receive for their product. Some states and/or growers' associations have set minimum acceptable levels for the presence of residual pits and pit fragments in processed fruit. The current allowed level for pits in dried plums processed in California, for example, is 0.025%, or 1 pit fragment for every 400 dried plums. To help achieve this level, fruit processors employ both hand inspection as well as imaging technologies such as machine vision and NIR spectroscopy. While this method helps reduce the number of pits and pit fragments, the problem is a persistent one for the industry. A better method or device is needed to supplement or replace existing technology and would benefit the industry as well as the consumer, with increased quality and product safety.
Efforts put forth by the California Dried Plum Industry are representative of how trade groups and their members are addressing the problem. Currently, this industry employs a combination of devices and proprietary techniques to rid fruit of pits and pit fragments. One popular device in use is the Elliot pitter, for example, which smashes the fruit between two rollers, squeezing the pit out (and sometimes crushing or cracking the pit itself, leaving behind pit fragments).
Another device in use is the Ashlock pitter which employs a conveyor system with mechanical cups holding each piece of fruit in place during the pitting operation. This device uses a pitting head comprised of eight needles, each of which pierces a dried plum and forces the pit out of the fruit and into a pit tube. Up to eight dried plums, therefore, can be pitted with each stroke of the pitting head, assuming each needle successfully engages a single fruit. When the machine is working properly very few pits are missed. However, when the needles are damaged or out of alignment, many pits can be missed or fragmented. The machine requires monitoring and quick maintenance in order to ensure efficient operation, and less than optimal performance can result in a large amount of pits being missed in a short time. Both of these devices, along with other techniques and devices in use, leave behind the occasional pit or pit fragment.
It is also noteworthy that use of the Ashlock pitting device results in the frequent deformation or disfigurement of the fruit being processed. The nature of the deformation depends on a number of factors, including the size of the fruit and its orientation as it passes through the pitter. In general, however, the removal of the pit results in the fruit being partially flattened or forced into a donut-shaped configuration (partially flattened with a hole in the center). Some processors attempt to restore the fruit as close as possible to its original shape. A processing method for fruit which involves temporary deformation, therefore, appears to be acceptable to the industry and is not considered “destructive.”
Once the fruit has been through the pitting process, it is necessary to test it for residual pits and pit fragments that may remain. Different methods and devices have been developed for this process and several patents exist on devices for detection of pits in fruit in general. So far, none of these devices adequately addresses the problem. Examples of how others have (inadequately) addressed the problem are set forth below.
One device which has been patented is based on transmission of visible light (U.S. Pat. No. 3,275,136 to Allen et. al., 1964) for detecting seeds in fruit, including cherries. This device suffers from frequent false positives which can be caused by blemished or unusually dense fruit.
U.S. Pat. No. 4,666,045 to Gillepsie and Ricks (1987) discloses a device based on transmittance and sensing of laser light for use with comestibles such as cherries, peaches and other types of fruit containing pits, but was never adopted by the industry due to a lack of accuracy (Timm et al., 1991).
Walsh et al. (1985) patented a device that impales the product with multiple pin-like projections that sense pressure differentials between the needles and the conveyor belt indicating the presence of a defect or irregularity. It seems likely that impaling each piece of fruit with multiple pin-like projections spinning on a wheel would cause damage to the fruit and be considered destructive. At the very least, such handling of the product is likely to lead to loss of quality and susceptibility to post-harvest disease.
Another device, described in U.S. Pat. No. 4,146,136 to Ross et al. (1979), forces the fruit between two rotating wheels to sense the difference in thickness between product with pits and that without. The device utilizes interlocking sets of wheels or rollers with non-adjustable square teeth which operate to impose a limitation on the size of the fruit being tested. The square teeth also appear to damage much of the fruit in the testing process. This device is not able to detect smaller or fragmentary pits, or pits of irregular size or shape (such as those which are irregularly flattened). Such a system also gives rise to many “false positives,” resulting in substantial amounts of acceptable product being unjustifiably rejected. The shortcomings of the machine appear to relate to it reliance on simply sensing the crude movement of the deflection of the rollers or wheels as a piece of fruit passes there between, and not on the actual measurement of the forces impinging on said rollers which provides for a much finer detection and control mechanism.
There are a number of patented devices that make use of physical sensors, including force transducers and accelerometers, to evaluate fruit quality, especially for ripeness and firmness. See U.S. Pat. No. 6,240,766 to Cawley (2001); U.S. Pat. No. 5,315,879 to Crochon (1994); U.S. Pat. No. 6,553,814 to deGreef (2003). All of these devices, however, are designed to evaluate the surface quality or density of the fruit and are not intended for detection of pits or pit fragments that lie deep within the fruit. The device described in the deGreef patent, for example, uses a series of wheels which “impact” or bounce off the surface of a rolling piece of fruit, measuring how hard or ripe the fruit is without regard to whether or not a pit or pit fragment lies at the core of the fruit being tested.
Considerable work has also been presented in the scientific literature for detection of pits in cherries. Moreover, the devices used to pit most cherries appear to utilize the same punch and die principle that the Ashlock pitter mentioned above, with the same problem of missed or fragmented pits making their way into the final product. It is plausible that a method that can detect pits in cherries may be applicable to other fruits, although there might be sufficiently significant differences between cherries and other fruits to render any solution to the cherry pit problem inapplicable to other fruits. Still, it is at least of academic interest to note how others have attempted to solve the problem of separating cherries from their pits.
NIR spectroscopy has been attempted to detect cherry pits (Law, 1973) but the results were fairly inconsistent and heavily dependant on fruit size and orientation. Attempts with x-ray have been marginal at best due to the small difference in x-ray absorption between the flesh and the pit at energies high enough to penetrate the product (Brown, as quoted by Timm et al. (1991)). A mechanical device that tests red tart cherries for pits has been reported (Haff and Schatzki, 1994, and Toyofuku and Schatzki, 1999), but this method involves pulping the product (and is therefore destructive) and would not likely be practical for most other fruits such as dried plums (prunes) for example. Finally, Nuclear Magnetic Resonance (NMR) has been used to identify pits in brined cherries (Zion et al., 1995). This method was found to be 97% accurate in classifying both pitted and unpitted cherries, but orientation was critical. Furthermore, NMR equipment is cost prohibitive and unlikely to be adopted by the industry.
Recent visits to several fruit processing plants, as well as communication with the Dried Fruit Association of California (DFA), indicates that none of the aforementioned devices have been adopted as an industry standard and that a reliable pit detection method is still required. In short, the problem of detecting pits and pit fragments in fruit has been surprisingly vexing. What is needed is a reliable and economical device and method that can be used to non-destructively detect pits in various fruits and to remove such affected fruit specimens from the product stream in real-time at a speed that is appropriate for use on-line.